ROCKLAND, Maine — Extremely high levels of E. coli, suspected of coming from dog waste, as well as a series of sinkholes, led city officials on Thursday to close the popular Snow Marine Park until further notice.

Interim City Manager Tom Luttrell said Friday that the decision was made Thursday to close the 14-acre park located off Mechanic Street. City councilors had been informed Monday night that the park might have to be closed because of test results that showed astronomically high levels of E. coli bacteria.

City workers spread lime around the park, the manager said, in an attempt to help neutralize the harmful effects of the animal waste. The workers had also gone around and cleaned up the dog waste that was on the ground.

While doing that, city workers discovered three sinkholes on the banking that leads from Mechanic Street to the park. Luttrell said the reason for the sinkholes was not known. Public works crews were at the park on Friday morning, trying to determine what was causing the holes to develop.

Luttrell said the park would remain closed until another round of E. coli tests can be done following the next rain. Once the park is reopened, no dogs will be allowed for a while.

City officials suspect that the contamination results from dog droppings. The park is considered an informal dog park where people let their pets run. A sample of surface water in the park found E. coli levels at 16,000. The level considered safe is 400.

Luttrell said the city has sent away a sample of the wastes to an outside laboratory to determine what species the E. coli originates. That test may take a month to get back.

While the park is closed to people and pets walking, people can still use the boat ramp to launch boats.